27017

Research and Development for Accracy Improvement of Neutron Nuclear Data on

Long-lived Radioactive Nuclei at KURRI-Linac

J. Hori, T. Sano, Y. Takahashi and H.Yashima

Research Reactor Institute, Kyoto University

INTRODUCTION: There are strong requests for re-

ducing the uncertainty of neutron capture cross section

data of minor actinides (MAs) to estimate the transmuta-

tion rate of those long-lived radioactive nuclei in the in-

novative reactor system. In recent years, intense pulsed

spallation neutron sources such as J-PARC[1], n-TOF[2]

and LANSCE[3] facilities became available to remarka-

bly improve the precision of neutron TOF data. However,

there are discrepancies out of a range of tolerance be-

tween current experimental results. It is understood that

the unrecognized systematic errors make a difference. In

order to recognize and reduce the systematic errors, the

project entitled as “Research and development for Accu-

racy Improvement of neutron nuclear data on Minor AC-

tinides (AIMAC)” has been started. In this project, we

aim at obtaining the resonance parameters precisely of

MAs by combining the neutron capture -ray measure-

ment to transmission neutron measurement at

KURRI-Linac. In this year, new detection system of neu-

tron capture rays and transmission neutron was con-

structed and its performance was confirmed.

EXPERIMENTS: We constructed 4 bismuth germi-

nate (BGO) scintillation detectors composed of 12 BGO

cylindrical crystals having 2 inch. in diameter and 2 inch.

in length for measurement of neutron capture rays. On

the other hands, a 6 mm thick GS20 6Li-glass scintillator

was used as a transmission neutron detector.

In the performance test, we used a sealed MA sample of 237

Np. Neptunium oxide powder of 1.13 g packed in an

aluminum disk container of 30 mm in diameter and 0.4

mm thick wall. The sample was placed in the geometrical

center of the BGO detectors using an aluminum sample

folder. To decrease the constant background due to decay

rays from radioactivity (26 MBq) of 237

Np, a 3 mm

thick lead shield was inserted in the sample folder and

BGO detectors. A distance between the sample and the

KURRI-LINAC neutron source was 10 m. To obtain the

incident neutron spectrum, a 10

B sample was also used.

Transmission neutron spectra with and without the 237

Np

sample were measured by the 6Li-glass detector.

RESULTS: Preliminary result of neutron capture cross

section of 237

Np is shown in Fig. 1. The relative cross

sections were normalized to the evaluated value of

JENDL-4.0[4] at 0.0253 eV. A correction of neutron mul-

tiple-scattering and self-shielding in the sample has not

be made yet. Although the amount of measuring time is

about one hour, enough net counts were obtained in the

resonance region. Comparison of transmission neutron

spectra with and without 237

Np sample by the 6Li-glass

detector is shown in Fig. 2. We could observe the signifi-

cant differences between those spectra with a high signal

to noise ratio..

The results show that the developed capture -ray and

transmission neutron detection system has a high perfor-

mance to determine the resonance parameters.

Fig.1 Preliminary results of neutron capture cross section

of 237

Np

Fig.2 Comparison of transmission neutron spectra with

and without 237

Np sample by the 6Li-glass detector

Present study includes the result of “Research and De-

velopment for accuracy improvement of neutron nuclear

data on minor actinides” entrusted to the Japan Atomic

Energy Agency by the Ministry of Education, Culture,

Sports, Science and Technology of Japan (MEXT).

REFERENCES:

[1]M. Igashira et al., Nucl. Instrum. Meth., A 600, 332 (2009)..

[2]U. Abbondanno et al., Phys. Rev. Lett. 93, 161103 (2004).

[3]M. Jandel et al., Phys. Rev. C 78, 034609 (2008).

[4]K. Shibata et al., J. Nucl.Sci.Technol.,48, 1 (2011).

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27050

Activation Measurements of Neptunium-237 at KURRI-Linac

S. Nakamura, K. Terada, Y. Shibahara1

, A. Uehara1,

T. Fujii1, T. Sanao

1, Y. Takahashi

1 and J. Hori

1

Japan Atomic Energy Agency 1Research Reactor Institute, Kyoto University

INTRODUCTION: A series of experiments with an

activation method has been performed to measure ther-

mal-neutron capture cross-sections of Minor Actinides

(MAs) under the project entitled by “Research and de-

velopment for Accuracy Improvement of neutron nuclear

data on Minor ACtinides (AIMAC)”. Neptunium-237 is

one of important MAs because it contributes to the

long-term radiotoxicity of nuclear wastes. Then, the pre-

sent work performed cross-section measurements of 237

Np by an activation method with a neutron source

generated by the KURRI-Linac.

EXPERIMENTS: A standardized solution of 237

Np

(4 kBq) was pipetted on a quartz plate (10mm×15mm×2mm

t), and dried by an infrared lamp. Then, the Np sam-

ple was put into an aluminum target holder together with

Co and Au foils as neutron monitors. The target holder

was set near the moderator tank at the target room of

KURRI-Linac. The irradiation was performed for 14

hours. The KURRI-Linac was operated under the condi-

tion: repetition rate 50Hz, pulse width 4s, 108A beam

current and 3-kW power.

After the irradiation, induced activities of the samples

were measured with a high purity Ge detector. Figure 1

shows an example of -ray spectrum of the irradiated 237

Np sample.

Fig.1 -ray spectrum of the irradiated 237

Np sample

RESULTS and DISCUSSION: Neutron flux compo-

nents were derived from the induced activities of the

monitors on the basis of the Westcott’s convention[1].

The thermal-neutron flux was 2.97×108(n/cm

2s) at the

irradiation position of 3-kW operation. The epi-thermal

index was 0.053. The reaction rate of the 237

Np sample

was calculated with 312-keV and 984-keV -ray yields,

detection efficiencies, decay data and -ray emission

probabilities. The reaction rate was (7.12±0.25) ×10-14

(1/s). The experimental reaction rate was compared with

the calculated one with evaluated nuclear data of 237

Np.

The neutron flux distribution at the irradiation position

was calculated by MVP2.0[2] with JENDL-4.0[3], and

plotted in Fig.2. The calculated flux was normalized

with the reaction rate of Au monitor. With the normalized

neutron flux and the cross-section data 237

Np from

JENDL-4.0[3], the calculated reaction rate resulted in

(7.41±0.14)×10-14

(1/s). The calculated reaction rate

was good agreement with the experimental one within the

limits of error.

Fig.2 Neutron flux distribution calculated by MVP Codes

CONCLUSION: Since the thermal-neutron flux was

found to be 108 (n/cm

2s) order, activation measurements

would be possible under adequate experimental condi-

tions: irradiation time, repetition rate, beam current and

so on. The activation measurement of 237

Np was per-

formed. It was found that this measurement supported the

evaluated data of JENDL-4.0.

The authors would like to thank staffs of Kyoto Uni-

versity Research Reactor Institute for their support.

Present study includes the result of “Research and De-

velopment for accuracy improvement of neutron nuclear

data on minor actinides” entrusted to the Japan Atomic

Energy Agency by the Ministry of Education, Culture,

Sports, Science and Technology of Japan (MEXT).

REFERENCES:

[1]C.H. Westcott et al., “Proc.2nd Int.Conf.Peaceful Use

of Atomic Energy, Geneva”, United Nations, New

York,16, p.70 (1958).

[2]Y. Nagaya et al., “MVP/GMVP II: General Purpose

Monte Carlo Codes for Neutron and Photon Transport

Calculations based on Continuous Energy and Muti

group Methods”, JAERI 1348 (2005).

[3]K. Shibata et al., J.Nucl.Sci.Technol.,48, p.1 (2011).

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27052

Development of the Epi-Thermal Neutron Measurement Method Using a Thick Boron Sample

T. Matsumoto, A. Masuda, H. Tomita1, K. Ito1, Y.

Ichinose1, T. Iguchi1, K. Watanabe1, A. Uritani1, J. Hori2

and Y. Sakurai2

National Metrology Insitute of Japan, National Institute

of Advanced Industrial Science and Technology 1Department of Engineering, Nagoya University 2Research Reactor Institute, Kyoto University

INTRODUCTION: Evaluation of neutron fluence and

neutron dose equivalent for the epi-thermal neutron re-

gion is very important in work places with neutron

sources or nuclear fuels as well as irradiation fields in a

boron neutron capture therapy. The epi-thermal neutrons

are usually measured using a gold activation detector, a

gas proportional counter or a scintillator. However, it is

not easy to determine precisely the neutron fluence for

the epi-thermal neutrons in an irradiation field because of

large uncertainty of reaction cross sections in the

epi-thermal region. In the present study, we have de-

veloped an epi-thermal measurement method that is not

affected by nuclear reaction cross sections. We also de-

veloped an epi-thermal neutron camera consisting of

GEMs and resonance filters for neutrons up to 10 keV.

EXPERIMENTS: A collimated neutron beam was

obtained by the photo neutron reaction using a wa-

ter-cooled tantalum target at the KURRI Linac [1].

Characteristics of a neutron detection system composed

of a 6Li6natGd10B3O9:Ce+ (LGB) scintillator and an

NaI(Tl) scintillator were experimentally evaluated by

means of the time-of-flight (TOF) method. The 50

mm-diameter and 5-mm thick LGB scintillator was set at

the center of the beam line. The 76.2 mm-diameter and

76.2 mm thick NaI(Tl) was located out of neutron beam

at an angle of 135 or 90 degrees with respect to the neu-

tron beam direction. When the LGB scintillator detects

neutrons by the 10B(n,γα) reaction, 478 keV monoener-

getic gamma rays are produced and subsequently detect-

ed with the NaI(Tl) scintillator. Moreover, the absolute

neutron fluence is determined by measuring gamma rays

from the 10B(n,γα) reaction with the NaI(Tl) scintillator

in setting a 5-cm thick natB total absorption sample in

front of the LGB scintillator. Number of alpha particles

and gamma rays produced by the 10B(n,γα) reaction in

the LGB scintillator are absolutely determined by the

coincidence measurements. Uncertainty caused by the

cross sections of the 10B(n,) reaction is reduced by us-

ing the boron total absorption sample. RESULTS: Fig.1(a) and (b) show ratio of the pulse

height spectra and the TOF spectra of the NaI(Tl) detec-

tor with and without the thick natB total absorption sample.

In Fig.1(a), 478 keV gamma rays due to the 10B(n,) reaction is detected around 600 channel.

These figures indicate the relative ratio of count

rate of the NaI(Tl) scintillator with and without

the boron total absorption sample. In the meas-

urements, it was confirmed that the present de-

tection system derived the neutron fluence in the

thermal and epi-thermal region.The experimental

results will be basic data in order to develop a novel

portable epi-thermal neutron detector.

0 200 400 600 800 1000100

101

102

103

PH Channel

Co

un

ts/C

han

nel

without B samplewith B sample

(a)

0 500 1000 1500100

101

102

103

TOF Channel

Co

un

ts/C

han

nel

without B samplewith B sample

2s/channel

(b)

Fig.1. Ratio of (a) the pulse height spectra and (b) the

TOF spectra of the NaI(Tl) detector with and without the

thick natB total absorption sample.

REFERENCES: [1] K. Kobayashi et al., Annu. Rep. Res. Reac-

torinst. Kyoto Univ. 22, 142 (1989).

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27081

Measurements of Americium Isotopes by Activation Method at KURRI-Linac

S. Nakamura, K. Terada,

Y. Takahashi1, T. Sanao

1and J. Hori

1

Japan Atomic Energy Agency 1Research Reactor Institute, Kyoto University

INTRODUCTION: Neutron capture cross section

measurements have been conducted for Minor Actinides

(MAs) under the research project entitled by “Research

and development for Accuracy Improvement of neutron

nuclear data on Minor ACtinides (AIMAC)”.

Since americium-241 and -243 have relatively long

half-life as 432yr and 7370yr respectively, these isotopes

are important nuclides among MAs in terms of environ-

ment load reduction. This is why these two americium

isotopes were selected in the present measurements.

EXPERIMENTS: Americium-241, 243 samples were

sealed on Al plates with 22mm in diameter and 0.5mm in

thickness, respectively. Their active areas were 20mm in

diameter. The amounts of the samples were 583kBq for 241

Am, and 2MBq for 243

Am, respectively. Each Am

sample was packed into an Al target holder. Then, sets

of monitors of Au and Co foils were sealed at adequate

positions on the Al holders. Then, the target holders were

set near the moderator tank at the target room of KUR-

RI-Linac.

Figure 1 shows the irradiation set-up of the 243

Am tar-

get near the moderator tank at the target room of KUR-

RI-Linac. The 241

Am target was irradiated for 35 hours

under beam conditions: repetition rate 100pps, beam

width 4s, beam current 220A, and 6-kW power opera-

tion, while the 243

Am target was irradiated for 40 hours

under another beam conditions: repetition rate 50pps,

beam width 2.5s, current 67A, and 2-kW power opera-

tion.

Fig. 1 Set-up of the 243

Am target at the target room of

KURRI-Linac

After the irradiations, induced activities of the samples

were measured with an -ray spectrometer, and a high

purity Ge detector. Figure 2 shows an example of -ray

spectrum obtained by measurements of the irradiated 241

Am sample for 11 days. On the other hand, the 243

Am

sample was measured by the Ge detector. The -ray spec-

trum of the 243

Am sample was measured for 20 hours,

and is shown in Fig.3.

Fig.2 An example of -ray spectrum of the irradiated 241

Am sample

Fig.3 An example of -ray spectrum of the irradiated 243

Am sample

ANALYSIS and RESULTS: As for the 241

Am exper-

iment, the neutron flux was approximately 1.4×108

(n/cm2s) on the basis of the Westcott’s convention. From

the peak counts of 241

Am and 242

Cm in Fig.2, the rate of 241

Am(n,)242g

Am reaction was obtained as (8.63±0.80)

×10-14

(/s). As for the 243

Am experiment, the neutron

flux was approximately 9.0×107(n/cm

2s) at the target

position. The decay -rays of 744 and 898 keV of 244g

Am

(10.1h) were observed as shown in Fig.3. The target

amount of the 243

Am sample was obtained with the yields

of 228 keV -ray emitted from 239

Np in equilibrium with 243

Am. From the ratio of -ray yields of 744 keV of 244g

Am and 228 keV of 239

Np, the 243

Am(n,)244g

Am reac-

tion rate was obtained as (1.14±0.03)×10-15

(/s), which

only included statistical errors.

Furthermore, detailed analyses are underway for the 241

Am and 243

Am experiments carried out at KUR-

RI-Linac.

The authors would like to thank staffs of Kyoto Uni-

versity Research Reactor Institute for their support.

Present study includes the result of “Research and De-

velopment for accuracy improvement of neutron nuclear

data on minor actinides” entrusted to the Japan Atomic

Energy Agency by the Ministry of Education, Culture,

Sports, Science and Technology of Japan (MEXT).

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